Generally, a track chain of a track-type work machine such as a hydraulic excavator or a bulldozer is formed by connecting a plurality of track chain assemblies in an endless state. The track chain is wound around a drive wheel and an idler wheel that are arranged in a body frame of the track-type work machine with a predetermined distance therebetween. When each track chain assembly is engaged to a sprocket of the drive wheel and driven, the track chain is moved while being supported by carrier rollers and track rollers that are arranged in the body frame between the drive wheel and the idler wheel.
A track chain assembly disclosed in FIG. 7 of Patent Document 1 has been conventionally known. In the track chain assembly disclosed in the document, a track shoe is fixed to a connecting link pair in which a pair of track shoe connecting links is arranged in parallel to each other. A support shaft is fixed between end portions each of which is included in one of the track shoe connecting links, and a sleeve is fixed between the other end portions each of which is included in one of the track shoe connecting links. The support shaft of the track chain assembly is rotatably inserted through the sleeve of an adjacent track chain assembly. Accordingly, a plurality of track chain assemblies are connected to each other to form an endless track chain.
In the above-described track chain, the sleeve functions as a bearing member that rotatably connects adjacent track chain assemblies each other and also functions as a power transmission member that receives power transmitted from a sprocket by being engaged with the drive wheel. However, since the sleeve is fixed to the connecting link pair in the related art track chain assembly, the sleeve receives high surface pressure in a specific portion and slidingly contacts tooth surfaces of the sprocket when the work machine moves backward. Therefore, the sleeve of each track chain assembly may be unevenly worn in a relatively early stage. When this happens, a portion of the sleeve that corresponds to and is fixed to the support shaft is forcibly moved with respect to the support shaft so as to be turned over (this operation is referred to as a bushing turn). However, the turning-over operation is troublesome and increases running cost.
To solve such a problem, for example, a track chain assembly disclosed in Patent Document 2 has been proposed. In the track chain assembly, the sleeve provided between the track shoe connecting links is divided into three portions in an axial direction of the sleeve. Each end portion of the sleeve is fixed to a shaft hole formed on an end portion of one of the track shoe connecting links, and a middle portion of the sleeve is externally fitted to the support shaft of an adjacent track chain assembly so as to be rotatable. Accordingly, relative sliding of the sprocket and the sleeve is allowed when the sleeve is engaged to the sprocket teeth. This prevents wear of the sleeve at an early stage.
On the other hand, Patent Documents 3 and 4 disclose track chains provided with track chain assemblies having following configurations. Specifically, in Patent Document 3, an elastic plate made of reinforced rubber or other materials is attached to each track chain assembly with an iron plate at a front wall surface of the track chain assembly that is a part of a ground-engaging surface of the track shoe. A distal end portion of the elastic plate of each track chain assembly contacts an adjacent track chain assembly at a rear wall surface of the adjacent track chain assembly that is also a part of the ground-engaging surface of the track shoe. Accordingly, a space between the track shoes of the two adjacent track chain assemblies is closed and muddy water is prevented from entering the space.
In Patent Document 4, a laminate plate comprising a plurality of laminated thin plates is fixed to a non ground-engaging surface of the track shoe in each track chain assembly. The laminate plate is discretely welded to the non ground-engaging surface of the track shoe. In the laminate plate, the adjacent thin plates are discretely connected to fix to each other. In this case, when the track shoe vibrates, quite small positional deviation or space may be caused between the track shoe and the laminate plate and between the thin plates of the laminate plate. According to the occurrence of the quite small positional deviation or space, the vibrational energy is converted to thermal energy due to friction or collision between the track shoe and the laminate plate and between the thin plates of the laminate plate. Accordingly, vibration and noise due to the vibration are reduced.
In the configuration disclosed in FIG. 7 of Patent Document 1, the track chain assembly has the pair of links, the connecting shaft fixed between end portions at one end of the links, and the sleeve fixed between the other end portions each of which is included in one of the links, and has a rectangular shape having four sides. In the configuration disclosed in Patent Document 2, the track chain assembly has the pair of links and the connecting shaft fixed between end portions at one end of the links, and has a rectangular shape with one side positioned between the links being open. In the configuration disclosed in Patent Document 2, rigidity of the links is lower than the configuration disclosed in Patent Document 1. In other words, in the configuration disclosed in Patent Document 2, if a force acts on the open side between the links so as to enlarge the open side, stress is concentrated on portions of the links near the connecting shaft and the portions may be damaged.
Therefore, in the track chain assembly disclosed in Patent Document 2 having a configuration of the rotatable sleeve, the links are required to be formed to be strong. However, the track chain having the track chain assembly with a configuration of a non-rotatable sleeve is more widely distributed and used than the track chain having the track chain assembly with a configuration of the rotatable sleeve. Since the parts of the track chain assembly are expendable supplies, the parts are required to be common in the track chain assemblies having the sleeves with different configurations and required to have interchangeability. In this point, in the track chain assembly having a rotatable sleeve, it is preferable to avoid using a link having high rigidity and a specific structure.
Further, in Patent Document 3, the elastic plate attached to the ground-engaging surface of the track shoe closes the space between the track shoes of the adjacent two track chain assemblies, however, does not increase the rigidity of the links of each track chain assembly. The iron plate that is provided for attaching the elastic plate to the ground-engaging surface of the track shoe is provided to the track shoe in a cantilever like fashion to hold the elastic plate and does not contribute to increase of the rigidity of the track chain assembly. The iron plate is provided in a recess of the track shoe to avoid contact with the road surface, and the recess lowers the rigidity of the track chain assembly.
In Patent Document 4, the laminate plate that is fixed to the non ground-engaging surface of the track shoe reduces vibration of the track shoe and noise due to the vibration. However, since the laminate plate is supported by the track shoe so as to generate positional deviation between the track shoe and the laminate plate, the rigidity of the track chain assembly is not increased by the laminate plate.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-249973
Patent Document 2: Japanese National Phase Laid-Open Patent Publication No. 6-504747
Patent Document 3: Japanese Laid-Open Patent Publication No. 9-66870
Patent Document 4: Japanese Laid-Open Patent Publication No. 2000-219168